[Double orientation tuning of neurons of the primary visual cortex of the cat at various levels of alertness].

Orientation tuning (OT) of 225 visual cortex neurons was studied in immobilized cats by their responses to flashing light bars. It was found that 43% of neurons had monomodal OT and preferred the horizontal and vertical orientations, while 57% of neurons had double OT, i.e. they had main preferred orientation (PO) and additional PO (aPO). The mean angle between PO and aPO was equal to 71.4 +/- 2.4 degrees. In half of the cases the second maximum of OT was equal to the first one (mean: 0.7 +/- 0.03 from PO). Orientation characteristics of PO and aPO were practically identical. Under light and middle levels of narcosis half of the neurons with double OT became monomodal and 12% of monomodal neurons receive bimodal OT. Monomodal neurons had more often simple RF and invariance of OT to narcosis. The neurons with double OT had simple and complex RF equally often and their OT changed in narcosis. It is supposed that the neurons with double OT can be an angle and line cross detectors. Monomodal neurons may be the stable bench mark system of orientation coordinates. Interaction of these neuronal systems permits conducting an effective analysis of image features in the primary visual cortex.